Hooping consists in winding a reinforcing element around a tube, generally made of metal, in order to increase the resistance of the tube to the internal pressure without increasing its weight significantly.
The tube can be a metal tube, for example made of steel. The reinforcing element has a large longitudinal dimension in relation to its cross-section. It can have the shape of a strip, of a wire or of a metal section. The reinforcing element is generally made from fibers, wires or wicks, made of glass, carbon, aramid or steel, coated with a preferably thermoplastic polymer matrix.
The reinforcing element can be wound around the tube while introducing a tension therein. Thus, the element wound around the tube is subjected to tensile stresses. The stresses introduced by the reinforcing element cause the metal tube or core to be stressed. The stresses undergone by the tube are radial in the direction of the axis of the tube.
The hooped tubes manufactured according to the method of the invention are notably used in the oil industry. Oil is produced from an offshore reservoir using a flexible or rigid pipe, generally referred to as riser, which allows the wellhead installed at the sea bottom to be connected to the surface. During well drilling operations, the riser forms the extension, through the water depth, of the casing carrying the oil from the well bottom to the wellhead. The riser is provided with at least two auxiliary lines called kill line and choke line, which are used to establish a hydraulic connection between the support at the sea surface and the wellhead at the sea bottom. More particularly, the auxiliary lines allow fluid to circulate below the closed blowout preventers in case of kick control. Each auxiliary line consists of an assembly of several identical tubes arranged parallel to an element of the riser tube.
In case of kick control, the auxiliary lines contain fluids under high pressure, about 700 bars for example. In order to limit the weight of the riser assembly, the hooped tube technique can be used for the auxiliary lines.
U.S Pat. No. 4,514,254 proposes hooping a tube by winding under tension a metal section around a tube. The tube thus hooped forms a vessel that has to withstand the stresses due to the pressure of the fluid contained in the tube. The tension of the metal section is so selected that, the vessel working under pressure, the stresses in the wall of the tube and the stresses in the metal section layers reach their allowable maximum value at the same time.